Production of iron powder



Patented Dec. 5, 1950 UNITED STATES PATENTOFFICE 7 PBQDUCTIDN OF IRON POWDER Herschel H. Cndd and Emma Jean Freeman,

East Point, Ga., assignors to International Minerals & Chemical Corporation, a corporation of New York N D a ng A p n Au u 17! 194.5.

' Serial No. 611,250

'acteristics are not without limitation in that it is conceivable that it might be possible to get the particles too porous or too dendritic, but in the known processes, the common .difliculty is the production of particles that do not have these characteristics to the extent desired for best results.

According to the invention, iron in finely divided form is precipitated electrolytically from an aqueous solution of an iron salt, for example a ferrous chloride or sulfate.

Concentration Temperature In the bath hereinafter described the quality of the deposit appears to be relatively independent of temperature over fairly wide limits. However, in order to produce a material of fine particle size it is advisable to employ relatively low temperatures, for example less than 40 C.

Electrodes In the bath hereinafter described it is not necessary to rotate the electrode or employ mechanical means for removing the deposit from the electrode. The deposit is so lacking in adherence thata great deal of it falls off of its: own

accord and a very slight agitation or'sti-rring will remove the rest. For instance, .meretremoyalnf the contents of the bath at a reasonably rapid rate will generate enough turbulence :to wash the remaining deposit off the electrode.

e'urren't density Satisfactory operation is easily obtainable as low as 25 amperes per square foot if sufiicient modifying agent is added to the bath. A material reduction in particle size results from usin higher current densities, for example as high as 2.4.0 amperes per square foot. With suitably designed cells it is not difiicult to deliver 140 amperes per square foot without excessive power loss.

M Qdifying' agent The modifying agents added to the bath to secure the unique fine grained dendritic deposit according to the invention include various materials which serve as foaming agents in iron salt solutions. A considerable variety of these agents have been tried and they all appear to be effective to some extent although some of them are materially better than others. Among the materials which have been used with appreciable advantage are the hydrophlllc colloids 5110;} as saponins, peptones, gelatins. albumins, pectins and casiens.

Best results so far have been secured from saponin prepared from Chile soap bark, but substantially equal effectiveness has been secured with a saponin in the form of pure digitonin. The digitonin we have employed is a white crystalline substance which on acid hydrolysis splits into one mol of digitogenin, four mOls of galactose and one mol of xylose. It is soluble in water and very soluble in methanol and hot ethanol. It has a specific rotation of in methanol. Anotheridentifying test is that, on the a..er'a e, 1,000 milligrams will precipitate 330 milligrams of cholesterol in 100 cc. of ethyl alcohol.

Ac d y Best results have been obtained so far when the pH is about 1.8 to 2.0 but a substantialvariation from this figure does not materially impair the results. For example good results have been obtained with a pH of 1.0 to 3.0.

Size control The grainsize decreases rapidly with increase in the percentageof foaming agent in the bath. For instance, in one specific examplaa bath con.- taining 0.1% of saponin and Operating at 26 gave the screen analysis in the middlecolumn of the following table, while a bath otherwise ;i d en tical-except-thatitcontained;0.3 .ofsaponin and operated at the same temperature gave the analysis in the right hand column:

0.1% 0.3% Mesh saponin saponin Per cent Per cent Does not pass 20... 18. Between and 45 55. 0 9. Between 45 and 65 16. 2 34. 6 Between 65 and 100. 5. 6 19.8 Passes 100 5. 3 35. 8

' in the solution being electrolyzed may be varied from about 0.1 to about 0.6 per cent, the larger the percentage of modifying agent, the smaller the particle size of the iron powder which is formed.

Recovery from the bath Separation of the precipitated metal from the liquid is not diflicult, but obvious precautions need to be taken to guard against oxidation or even explosion. Especially in the finer grain sizes the product is decidedly pyrophoric and may ignite with destructive violence if dried and exposed to air. A satisfactory procedure is to filter and wash the residue first with ordinary water then with a .1% solution of ammonium carbonate or hydroxide, and finally with water which has been freshly boiled to eliminate dissolved oxygen. After this washing the product may be reduced to dryness in the absence of oxygen. If desired, the particle size may be further reduced by grinding under non-oxidizing conditions in any suitable mill. To obtain a very soft pure product, it may advantageously be annealed in hydrogen.

The process as described is of particular value for producing an iron powder in which the particles are of small size, and in a highly porous or dendritic condition. It may be used without grinding in the production of pressure-molded parts, particularly sintered parts.

Without further elaboration the foregoing will so fully explain the invention that others may adapt the same for use under various conditions of service.

What is claimed is:

1. The improvement in the art of producing iron powder, which comprises: electrolyzing an aqueous solution of an iron salt selected from the group consisting of ferrous chloride and ferrous sulfate, said solution being at a pH of between about 1.0 and 3.0 and containing at least about 2.8 per cent of ferrous ion, said solution also containing at least about 0.1 per cent of a hydrophilic colloid, which in said solution, will function as a foaming agent, the current density during electrolysis being between about and 140 amperes per square foot.

2. The method of producing iron powder which is adapted for use in the fabrication of sintered parts, which comprises: preparing an aqueous solution of ferrous chloride which contains from about 7.0 to about 9.9 per cent ferrous ion and from about 0.1 to about 0.6 per cent of digitonin; adjusting the acidity of the solution to a pH of between about 1.8 and about 2.0; electrolyzing the solution to deposit iron as a dendritic powder by employing a current density of from about 25 to about amperes per square foot; and separating the iron powder from the solution, the size range of the dendritic iron particles being determined by the percentage of digitonin in the solution, the particle size decreasing with an increased concentration of digitonin.

3. The method of producing iron powder which comprises: preparing an aqueous electrolyte which contains at least about 2.8 per cent ferrous ion and at least about .1 per cent of a saponin, adjusting the acidity of the electrolyte to a pH of between about 1.0 and about 3.0; electrolyzing the electrolyte to deposit iron as a dendritic powder by employing a current density of from about 25 to about 140 amperes Per square foot; and separating the iron powder from the electrolyte.

e. The method of producing iron powder which comprises: preparing an aqueous electrolyte which contains from about 7.0 to about 9.9 per cent ferrous ion and from about 0.1 to about 0.6 per cent of a saponin, adjusting the acidity of the solution to a pH of between about 1.8 and about 2.0; electrolyzing the electrolyte to deposit iron as a dendritic powder by employing a current density of from about 25 to about 140 amperes per square foot; and separating the iron powder from the electrolyte, the size range of the iron particles being determined by the percentage of saponin in the solution, the particle size decreasing with an increased concentration of saponin.

5. The method of producing iron powder which comprises: preparing an aqueous electrolyte which contains at least about 2.8 per cent ferrous ion and at least about .1 per cent of Chilesoap-bark saponin, adjusting the acidity of the electrolyte to a pH of between about 1.0 and about 3.0; electrolyzing the electrolyte to deposit iron as a dendritic powder by employing a current density of from about 25 to about 140 amperes per square foot; and separating the iron powder from the electrolyte.

6. The method of producing iron powder which comprises: preparing an aqueous electrolyte which contains from about 2.8 to about 19.7 per cent ferrous ion and from about 0.1 to about 0.6 per cent of Chile-soap-bark saponin, adjusting the acidity of the solution to a pH of between about 1.0 and about 3.0; electrolyzing the electrolyte to deposit iron as a dendritic powder by employing a current density of from about 25 to about 140 amperes per square foot; and separating the iron powder from the electrolyte, the size range of the iron particles being determined by the percentage of saponin in the solution, the particle size decreasing with an increased concentration of saponin.

'7. The method of producing iron powder which comprises: preparing an aqueous electrolyte which contains from about 7.0 to 9.9 per cent ferrous ion, the salt supplying the ferrous ion being selected from the group consisting of ferrous chloride and ferrous sulfate, and about 0.3 per cent of Chile-soap-bark saponin; adjusting the acidity of the solution to a pH of between about 1.8 and 2.0; electrolyzing the electrolyte to deposit iron as a dendritic powder by employing a current density of from about 25 to 140 amperes per square foot; and separating the iron powder from the electrolyte.

8. The method of producing iron powder which comprises preparing an aqueous electrolyte which contains over about 2.8 per cent ferrous ion and over about .1 per cent of a digitonin, adjusting the acidity of the electrolyte to a pH of between about 1.0 and about 3.0; electrolyzing the electrolyte to deposite iron as a dendritic powder by employing a current density of from about 25 to about 140 amperes per square foot; and separating the iron powder from the electrolyte.

HERSCHEL H. CUDD.

EMMA JEAN FREEMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 949,004 Ramage Feb. 15, 1910 1,912,430 Cain June 6, 1933 Number Number Name Date Teats Oct. 24, 1933 Hardy May 9, 1939 Mantel Feb. 25, 1941 Bauer June 23, 1942 Brown Nov. 20, 1945 Stoddard May 13, 1947 Balke Mar. 8, 1949 Pike et a1. Mar. 22, 1949 Matson et a1. Aug. 30, 1949 FOREIGN PATENTS Country Date Great Britain May 14, 1930 OTHER REFERENCES Transactions of American Electrochemical Society, v01. 25 (1914), pages 529 to 532.

The Metal Industry, Oct. 7, 1938, page 350.

Certificate of Correction Patent No. 2,533,096 December 5, 1950 HERSGHEL H. CUDD ET AL. It is hereby certified that error appears in the printed Specification of the above numbered patent requlring correction as follows:

Column 2, line 25, for casiens read casez'ns; column 4, line 75, after the word comprises insert a colon; column 5, line 5, for deposite read deposit; column 6, list of references cited, under the heading OTHER REFER- ENCES add the following- The Journal of the Iron and Steel Institute, 001. 109 (1.924) N o. 1, pages 4 -4 4 and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 13th day of March, A. D. 1951.

THOMAS F. MURPHY,

Assistant Gommissz'oner of Patents. 

1. THE IMPROVEMENT IN THE ART OF PRODUCING IRON POWDER, WHICH COMPRISES: ELECTROLYZING AN AQUEOUS SOLUTION OF AN IRON SALT SELECTED FROM THE GROUP CONSISTING OF FERROUS CHLORIDE AND FERROUS SULFATE, SAID SOLUTION BEING AT A PH OF BETWEEN ABOUT 1.0 AND 3.0 AND CONTAINING AT LEAST ABOUT 2.8 PER CENT OF FERROUS ION, SAID SOLUTION ALSO CONTAINING AT LEAST ABOUT 0.1 PER CENT OF A HYDROPHYLIC COLLOID, WHICH IN SAID SOLUTION, WILL FUNCTION AS A FOAMING AGENT, THE CURRENT DENSITY DURING ELECTROLYSIS BEING BETWEEN ABOUT 25 AND 140 AMPERES PER SQUARE FOOT. 